Minor updates

I removed the declarations of a few unused variables and added a couple of implicit nones.

I seem to get a warning when linking the shared lib with ifort, and I'm not sure what it means:

Linking Fortran shared library ../usr/lib/libPG2PLplot.so
ld: CMakeFiles/PG2PLplot_shared.dir/src/PG2PLplot.f90.o: warning: relocation against `pgpoly_' in readonly section `.trace'.
ld: warning: creating a DT_TEXTREL in a shared object.